Thursday, December 31, 2009

New Year's is rapidly approaching and so is a strong warm front (see satellite image above).Rain has now reached the south Sound and you can expect a relatively wet day. For those thinking of celebrating outside I have good news....most of the rain should be through by 10 PM...and with with warmer air and scattered showers, it won't be too bad to welcome the new year at the Space Needle or some other outdoor venue. I should note that it will be quite windy along the Oregon coast this afternoon (see graphic). This kind of situation can produce strong coastal accelerations and sustained winds of 20-40 kts and high gusts can be expected in that area.Sea level pressure (solid lines) and low-level temps (shading)

Winds shown by shading

Tomorrow will be showery and then Friday night a modest low will make landfall on central/northern Vancouver Island and move north of us (see graphic). It will be windy on the coast and offshore tomorrow afternoon, and as the low moves north of us (see next graphic) the pressure variations and winds will increase over the lowlands. However, but the winds will be modest (generally 10-25 kts) over the lowlands with higher gusts near water.

Saturday will have some showers and decreasing winds and then Sunday looks dry. Temperatures will be on the edge for snow in the passes today and tomorrow (there could well be several inches of wet snow before the temps warm enough to turn it to rain), but it will be cold enough for snow on Saturday in the post-storm showers.

The long term forecast is very interesting. A weak disturbance brings some light rain on Monday, but then a major ridge builds in the eastern Pacific and stays there for many days. We could completely dry out with no major weather for quite a while. Temperatures would be well above normal. Is the El Nino winter about to begin? I suspect most of our interesting winter weather will be behind us as we start 2010. And happy new year to those reading this blog...

Tuesday, December 29, 2009

And I am not talking about liquid refreshments. After a dry, and sometimes sunny period, we are about to see some serious rain again. Been almost a week.

Tonight we are getting some showers from a very weak front that is moving through (see radar image). And tomorrow there will be some scattered showers and even some sunbreaks--temps climbing into the 40s. Not too interesting.

But don't worry...meteorological fun is in store on Thursday. A fairly strong warm front will move up the coast during the afternoon and will pass over the central WA coast and Puget Sound around 4 PM (graphic). Winds will increase and temps will jump as it passes. Particularly strong winds will strike the Oregon coast behind the front. Moderately heavy showers will accompany the warm front--the 24h rainfall totals ending 4 PM on Thursday show that although western WA will be wet, the real soaking will over western Oregon and NW California (graphic). The subsequent 24-h will be equally as wet, with NW CA and SW Oregon getting inundated. (see graphic)Enough to make a web-footed Washingtonian happy? But wait, there's more!

The latest runs show a modest low pressure center approaching our area. The first graphic below shows the pressure pattern at 4 PM on Friday--with the low off the Washington coast. Big pressure changes and winds along its southern flank. The track of the low will be critical for who gets strong winds and who doesn't--and subsequent runs have been shifting the low southwards.

Tonight's run...the latest....takes it into NW Washington...which is good for windy conditions over Puget Sound (see graphic). The only problem is that the low is fairly weak...only 1000 mb ...so we can't expect much. Perhaps gusts of 20-30 mph.

Anyway, its good to be getting back into some active weather. And decent mountain snows on Friday and Saturday. I bet Jim Forman will have a good time.

Sunday, December 27, 2009

I was looking for an inexpensive vacation last week that offered lots of sun and interesting weather features--well I found one --Tucson, Arizona.

Perhaps my most interesting weather experience was ascending one of the "sky islands" - the Santa Catalina Mountains northeast of Tucson. Starting around 2500 ft in the Tucson metro area, one can take the Catalina Highway/Sky Island Scenic Byway to 9,157-foot Mt. Lemmon over about 25 miles (see map). This topographic "island" within the Sonoran desert provides a wide range of climatic and weather conditions, with temperature dropping and precipitation increasing with height.

We started in Tucson under sunny skies and temps about 55F--surrounded by Saguaro and other cacti. The Saguaro are the cacti that are so often used to represent the Southwest (one is shown in the figure below), but they really only found in southern Arizona and Mexico--they can't handle below freezing temperatures for any length of time. By around 4ooo ft the Saguaro were gone--just too cold.

Weaving up the road, the vegetation and climate changed rapidly, and by around 5000 ft we started to see some SNOW in shaded areas. By 6500 ft there was loads of snow and we had entered a pine forest--reminding me of the eastern slopes of the Cascades. Moving higher, the snow got deeper (perhaps 3-6 inches at 7500 ft) and the air temperature was probably around 35F. So in 45 minutes one goes from desert to snow and a northern-type forest...there is even a ski area at the top!

Average rainfall is roughly 12 inches in Tucson (slightly wetter than eastern Washington) to 30 inches at the Mt. Lemmon site (slightly drier than Bellingham).

But the weather excitement didn't end there. On Tuesday, Dec 22, a cold front was approaching central Arizona, with a low center to the north--the result was a large pressure difference over the region with winds accelerating to 40-50 mph. We were out hiking in Saguaro National Park as the wind hit and the most extraordinary thing was the rapid loss of visibility (see pic). The situation got very bad on I10 south of Phoenix where winds blew over agricultural fields. (it has been a very dry year...Tucson only has received about half their normal 12 inches a year). The result was a severe dust storm that resulted in over 20 accidents on I10, a death, and the temporary closure of the road (graphic).

The adaption of the plants and animals to the dry conditions is really extraordinary, including the ability of big cacti to store tons of water and the dual usage of cactus needles for both protection and shading. I was not a little disappointed about human adaption down there...lots of large vehicles and relatively few solar panels.

And my family's adventure in Tucson was really enhanced by the very nice bed and breakfast we stayed at: a place called Azure Gate. Friendly, helpful people and extraordinary food.

Finally, what about our weather? Our sunny period ends today...and tomorrow will bring increased clouds and a few sprinkles. Then a few weak systems in store...but nothing of any note for several days. Unfortunately, for active weather lovers the influence of El Nino will now become more significant...and that means that weakened and split systems will be more frequent than normal...and snowpack should be below normal.

Thursday, December 24, 2009

Picture by Reid Wolcott of low clouds over the Puget Sound lowlands, taken from Newcastle Golf Course

How many ways can a meteorologists spell "Boring"? For the past several days we have been stuck in the classic mid-winter ridge pattern, when high pressure over the region produces dry, low wind conditions. The problem is that such conditions produce the hated, yes even despised, persistent low clouds and fog. Why? With a ridge there is a lack of clouds aloft and the surface can effectively radiate heat to space without the clouds getting in the way. The atmosphere doesn't radiate as well and the result is an inversion, with temperature increasing with height. Low wind speeds with the ridge result in a lack of good atmospheric mixing in the vertical, and thus a strengthening of the inversion.

Inversions act as barriers to air motion and as the air progressively cools near the surface, fog and low clouds can form. Moisture collects below the inversion, strengthening the fog. And wait! It is even worse than that! The top of the clouds are very effective in radiating heat to space....so you get cooling there, which mixes down into the cloudy layer. If the cloudy layer is thin enough, some sun can get through to "burn" if off. Fog burns off in two ways----from the outside perimeter towards the interior and from the bottom up. We didn't understand how fog burned off from its edges until weather satellites showed this to us. The burning off from the bottom results in fog "lifting" into stratus.

When there is fog around, Sea Tac is often enshrouded (and operations affected), while Boeing Field and Portland are operational. Why? Sea Tac is high--roughly 450 ft up---and when the clouds start lifting in the region, they can still be in the soup while Boeing Fields gets enough low-level cleaning to allow the airport to open. Portland has the advantage of air jetting out the Gorge...which can mix things enough to stop fog formation. In any case, it is always wise to fly as late as possible in the winter from Sea Tac, when fog is least frequent.

And when fog and cold are around, there is another threat to think about ....black ice on the roadways....so be careful.

Computer models indicate this general pattern should hold into next week. Not my favorite weather pattern. And one that doesn't improve our declining snowpack. Right now the snowpack is below normal for increasing portions of the region (see graphic)...and with El Nino effects strengthening after Jan 1, a little pessimism is in order for skiing and water supply.

Monday, December 21, 2009

There were quite few comments on my Climategate post last week. There was a bit more I wanted to say and will do so here.

My bottom line message was that anthropogenic global warming (AGW) IS a major problem, but one that has received considerable hype from both "sides." One side is convinced, for good reason, that AGW is a real problem, but is not afraid to dramatize the threat a bit or to see the "other side" in threatening terms. The other believes the whole business is some kind of false science inspired by some left wind conspiracy. Or they repeat ideas that don't hold water under examination: e.g., that since the earth has had climate cycles before, we can't pin changes on greenhouse gases. Or that since we can't forecast weather well next week, how can we predict climate change fifty years from now? Or that there can't be global warming caused by man because the earth's temperatures haven't changed much during the last 5-10 years.

If we had some magic technical fix for AGW (e.g., a cheap and effective process to remove CO2 from the atmosphere, or fusion power was made practical tomorrow) that would still not fix the really serious problem...sustainability. There is simply too many people on our planet and there will soon be a lot more. All want to enjoy the high standard of living in the western world--and how can we deny them what we have? We can't--they have as much right as we do for a comfortable life. We are using up the planets fresh water, exhausting the soils, polluting the air and ocean, using up limited resources (like oil)..the list goes on and on. Our species can't expand our numbers forever and we have to find a way to live indefinitely with the planet's carrying capacity.

Getting back to the Copenhagen meeting. It has been clear for a long time that no nation is willing to hurt its economic development in the short term for ameliorating a theoretical problem mainly in the future. Kyoto was pretty much of a joke in terms of doing anything serious and the agreement of last week lacks concrete measures. Even people who are emotionally committed to doing something about AGW are unwilling to change their personal lives in a meaningful way. How many global warming activists are jetting across the world for seemingly endless meetings? I know some with vacation homes--the ultimate waste of resources. If such committed people won't sacrifice and are not a little hypocritical, how can we expect others to?

Lets be honest with ourselves...there is only a few ways left to proceed now:

1. Put large amount of resources into technological improvements in energy efficiency, new energy sources, removal of Co2 from the atmosphere, etc. Make it cost effective and NO SACRIFICE to reduce fossil fuel emission. Green industry can be a boon for everyone. The U.S. is very rich in solar and wind energy...we are just scratching the surface. And we and much of the world waste huge amounts of energy. Obama should make this a priority---a Manhattan Project like effort.

2. Take serious steps on adaption--making the changes necessary to reduce the impacts of global warming and to take advantage of the good things that go with it. And there will be good things. The Canadians and Russians are going see vast areas opening up to agriculture. Washington State wines will get even better (sorry Californians).

Taking both approaches will help give us time to deal with the overarching problem...sustainability and overpopulation.

But there is something else we have to do educate ourselves better. Too many people on both sides of this are expressing opinions without really understanding what they are talking about. The climate system is extraordinarily complex and people learn a few facts and think they understand more than they do. For example, most people don't understand about natural variability..how the atmosphere has variations without any external cause, like increasing greenhouse gases. Thus, it is possible for temperatures to remain steady or even decline for a few years under increasing greenhouse gases...if the natural variability is on a downward turn. A year ago I explained this to a leading "free market" environmentalist who never understood this fact....I could see the impact this simple (or not so simple) idea had. And global warming activists need to do some learning too...how many times have I heard simplistic arguments that warmer temperatures will cause increased humidity and increased severe precipitation everywhere. Just not true.

And scientists must do a far better job at explaining things...in an open and non-patronizing way. Communication has to be seen as an essential part of our job, and we need to be more open with the uncertainties--what we are not sure about.

Saturday, December 19, 2009

Here is the six hour forecast valid 10 PM tonight (Saturday) with sea level pressure (the solid lines) and precipitation. Two coasts, two storms. For us, a warm front is now moving through the region, and you can see the band of precipitation associated with it on a recent radar image (graphic). Temps will warm up as the warm front pushes north. Then late tomorrow the cold front front will hit us, with substantially increasing precipitation (see 24-h amounts ending 4 am on Monday). Unfortunately, it has been warm enough to rain in the mountains...not very good for the snowpack. More Cascade-concrete in the making!In contrast, the east coast is getting a powerful, but tightly wound, Noreaster. Strong winds and heavy precipitation along the coast areas..with temps cold enough for snow. What does that spell? Blizzard. DC has already gotten over a foot and some locations are getting as much as two feet. Eastern LI should really get it. Here is the current radar for the New York area...see how nice it is to have a coastal radar to see precipitation moving in from offshore...or seeing approaching low centers?....in a few years, we will have it to.

Thursday, December 17, 2009

Today, President Obama signed the 2010 Appropriation Bill with 7 million dollars for a coastal radar for the central Washington Coast. That plus the funds already made available in the stimulus funding earlier this year (2 million dollars) will completely fund all costs for purchasing and installing a high-powered, state-of-the-art radar that will greatly improve our ability to see weather systems approaching our state. It will allow us to clearly determine the amount of precipitation falling on the southwest side of the Olympics and over the mountains of SW Washington. Its view will extend to the entrance of the Strait of Juan De Fuca and the Columbia River. By defining the weather coming in from the west, it will result in improved prediction over the entire state.A great deal of credit is owed to Senator Maria Cantwell, who did the heavy lifting in securing the funding for this critical piece of meteorological infrastructure. And the rest of our state delegation was highly supportive. Her press release is found at:http://cantwell.senate.gov/news/record.cfm?id=320986

Using the earlier stimulus funding, a National Weather Service site survey team has been hard at work evaluating potential sites, and a public report is due very soon, with three possible sites. I have seen draft documents and the locations look very good.

The radar will be a powerful "S-band" radar like the Camano Island radar, but it will be a modern device that has the polarization option that will be added to the current radars. This option allows much better determination of precipitation rate and the type of precipitation. The radar will become part of the National Weather Service network, and many of hope its configuration will be optimized for use in our area. That includes zero degree elevation angle scans to see further and up and down scans (RHI scans) to provide more information of atmospheric structure and freezing level.

The current timelines for the radar is for installation in late 2012. A number of us believe that a more aggressive schedule would allow the radar to be installed 6 months to a year earlier.

This is a major advance for my profession and the safety/protection of our region.

Tuesday, December 15, 2009

Several of you have asked me during the past few weeks to comment on Climategate--the emails stolen from the University of East Anglia dealing with global warming issues. I will do so here, but I want to go beyond that situation to some of my own personal observations derived my own experiences doing climate-related research.

Let me start with my bottom line points:

Were some of the climategate emails inappropriate? YesHave some scientists exaggerated the implications of human caused global warming? Yes.Are many global warming deniers unreasonable and expressing opinions that are not based in facts or rational thought? Yes.Is the basic science of climate change now in question because of the climategate emails? No.Has the whole business gotten too political? Surely.Are scientists human and sometimes doing things out based on human emotion or group think? Yes.

Climategate emails: I read through more than a hundred of them...particularly the ones that have gotten big attention. These scientists were in circle the wagons mode. Clearly, they felt under pressure, if not threatened, by the global warming (GW) skeptics, and discussed ways of denying the critics information requested through Freedom of Information inquiries. They scientists talked about erasing emails, and not publishing in journals they felt were printing materials they disagreed with. Web sites like "Climate Audit" has become dirty words to some. (I personally love "Climate Audit"!). All of this was inappropriate.

In the famous "trick" email the east Anglia emails talk about replacing the proxy tree ring records with instrumental records for the past several decades (because the tree ring records disagreed with what the instrumental records were saying)--instead of just showing those records and noting the difficulty. Not quite open. Is there any major technical cover up evident in the emails?...not that I could see. Denier and skeptic types are claiming that these emails undermine the whole global warming business...and they are completely wrong about that. But there are some general issues we should talk about.

There is an almost tribal separation going on today between the scientific community and their "allies" (generally of a liberal persuasion) and the denier and critic crowd (many of them of a conservative bent). The denier folks have become angry, with conspiracy theories and accusations of far-left agendas. Whenever there is an article on climate change in newspapers, these people leaves large numbers of online comments. And few of them are well informed about the science. And there is a lot of misinformation on the "pro" global warming side as well. Scientists, unaccustomed to being on the firing line, have gotten defensive--and the emails from climategate really document this attitude.

This defensiveness has now gotten unhealthy for both the science and society. Scientists who attempt to publish material indicating that global warming due to manmade causes is not evident or weak, or who doubt the severity of the problem, are not treated well by some. I have had some first-hand experience with this. I am known as somewhat of a skeptic regarding global warming effects in the NW--although I do believe that greenhouse gases are a serious problem in the long-run. A group of us noted that the snowpack in the Cascades was NOT rapidly melting away, in contrast to some publications by some local climate scientists and publicized by Mayor Nickels. The reaction was intense. One of my colleagues, Mark Albright, who was the first to notice the lack of snowpack loss was fired as associate State Climatologist and the media went wild...we called it Snowpackgate...and it got national attention. I was told in the hallways to keep quiet about it...the denier types would take advantage of it!

We then wrote a paper on the subject (the main contributor being Mark Stoelinga) and submitted it to the Journal of Climate. I have published a lot of papers in my life (roughly 100) and I never had problems like we had with this paper. Very biased associate editor and some reviewers. Four review cycles and it was about to be turned down, until we appealed to the editor, who proved fair and reasonable. This paper has now been accepted for publication, but it really revealed to me the bias in the system. Here is the paper if you are interested:

Poor papers with significant technical problems, but reflecting the "official" line, get published easily, while papers indicating the global warming is weaker or delayed, go through hurdle after hurdle.

I have heard case after case of similar treatment...so this is no anomaly.

The media tends to publish all kind of threatening predictions about global warming without really researching them. A good example is that suggestion that heavier precipitation will fall in the NW under GW...or is already happening. There is no evidence for this, but it gets repeated over and over again. On the other hand the denier types point to every cold wave or the fact there has NOT been a lot of warming in the last 5-10 years (which doesn't mean anything). And the glaciers! Some of the melting may well be due to man-forced warming...but the melting started early in the last century before CO2 effects were significant.

Another problem is that uncertainty of our climate predictions are often not clearly expressed in various publications--even semi-official ones put out by climate impacts groups of various types. It is sobering to note that the uncertainty in climate predictions has not declined over the past decades. Our models are much better now than thirty years ago, but key aspects of the modeling systems...like how they simulate clouds... are not as realistic as we would like...and this is very important for climate change work. I think people sense there is more uncertainty in the predictions than the official outlets tell them...and that may be part of the fuel of denier rage. The essential physics of warming is quite solid and well understood, but the details...like how clouds will react...are still under investigation.

So perhaps I have been confusing....but the bottom line is that this issue has been completely politicized and confused with both sides using problematic information at times....did this have to happen? If Gore hadn't taken up the mantle of stopping global warming, would things have been better? Can Climategate lead to a better approach and attitude among all parties?

PS: Talking about "Secrets of Snow" at Third Place Books tonight...Lake Forest Park... 7 PM

Monday, December 14, 2009

It is snowing in Eastsound on Orcas now and ice pellets are raining on Bellingham. On the other hand, for the rest of us there is moderate rain and rapidly warming temps.Check out the latest radar...you haven't seen wet like that in a while.

And here are the latest surface obs. The approaching low is sucking air out of the Fraser River Gap with cool NE flow moving into Bellingham and the San Juans. Won't last forever--eventually they will turn to rain too.Why? Because a warm front is approach (see graphic) and when it passes through warm, strong sw flow will inundate the region. You will feel like you have gone to Hawaii...well, sort of.

This figures provides temps in the lower atmosphere..yellow is warm and blue and white are cold. Also pressures and winds.

Snowing in the mountains (see cam at Snoqualmie)...and they are going to get hammered..which is really good for all you skiers.

PS: A reminder--I will be giving a talk.."The Secrets of Snow" at 7 pm at 3rd Place books in Lake Forest Park on Thursday, Dec 17th.

Sunday, December 13, 2009

Most of this "snow event" is over folks, except for some moderate snow showers north of Everett for convection elements moving through the Strait of Juan de Fuca. Sorry to all snow lovers.

Next fun..the warm front tomorrow. The main snow threat for that will be south and southeast of the Olympics and near Bellingham..before it turns to rain they could get a few inches. And then plenty of snow in the mountains...skiers will be happy!

We had a bit of light snow around the region, mostly flurries, although Bellingham and Olympia had enough to whiten things up (image)

As the radar shows, central Puget Sound is rainshadowed by the Olympics, which is what you expect under this situation (winds aloft are westerly and northwesterly). The upward motion from the upper trough (which brought the earlier snow showers) is quite weak. The convergence zone is weak since it doesn't have good low-level support (winds along the coast are not strong NW as you would like).The convergence zone may rev up a bit later. So we have some light snow in the south Sound, in the weak convergence zone, and over NW WA. The coast is getting a few rain showers (a little too warm there). Mostly flurries, but north and south of the snow shadow the ground may whiten with perhaps a 1/2 inch of snow.

Saturday, December 12, 2009

This morning's run is now in. Today will be snow free for most of western WA...only the Portland suburbs could see a few snow showers and some freezing rain.

The new model runs are somewhat more threatening for the Seattle metro area. The front associated with the upper shortwave (see figure) will come in mid to late afternoon. It is producing more of a trough/low at the surface then earlier runs and now the model suggests light snow over central Puget Sound (see graphic). Not a lot, but enough to whiten the place. Timing--starting roughly 3 PM and continuing for three to six hours. Then whatever snow is left would be in the Puget Sound convergence zone north of the city.

Next threat will be Monday evening with the warm front--could start as snow, with only NW WA getting anything significant (few inches) before it turns to rain as the air warms up.So today is fine...hit the malls, visit friends, or go to your favorite concert or activity.Tomorrow is ok till roughly 3PM. Then be careful...this is not going to be a big snowstorm--an inch or two at the most.Monday is fine. Monday night when you are home there could be some light snow turning to rain Tuesday AM. Commute will be fine Tuesday.

PS: I will be giving a public lecture--"The Secrets of Snow"--at Third Place Books in Lake Forest Park on December 17th at 7 PM, followed by a book signing. In this talk I will describe the unusual circumstances that have to come together for us to get a big snowstorm, details of convergence zone snows, the Fraser River Gap flow, arctic fronts, and more. My favorite topic

Friday, December 11, 2009

I just finished watching part of the 11 PM broadcast of a local TV station. Pushing snow way too much. And then they show the typical snow scare sequence:

1. The ominous warning2. The snow plows gassing up3. The big pile of salt and sand4. The supermarket with people rushing to stock up5. The tire store with people desperately trying to get snow tires.

Perhaps they film this once and reuse it each storm.

The new models are in and are consistent with the last runs.

Portland and vicinity will probably get up to an inch or two of snow on Saturday.Seattle will get nothing tomorrow.

Sunday is the day. A trough is coming...but there is little meteorological "juice." The trough is too far eastward. Cold air will push in through the Fraser valley. A combination of the arctic front and a weak convergence zone (actually two convergence zones..one in the lee of the Olympics, the other in the lee of Vancouver Is), coupled with the trough, could produce some snow from Seattle into NW WA. Some locations might get an inch. Or less. And the snow could occur into early Monday morning. Could start around 3-4 PM on Sunday

Then we have another chance late Monday as the warm front comes in....but if it starts as snow it will end soon as warm air streams in on Tuesday.

Anyway, some of you will see snow, but many of you will see nothing. I really like snow and wish for a big event...but this ain't one...or at least it doesn't look like it to me.

Latest models are in. Some of you will see snow. But no big snowstorm that will last for days.

The first with snow will be the northern Willamette Valley and Portland environs, which should catch some light snow from precipitation moving up from the south. It won't get north of Centralia.

Then on Sunday an upper trough will move through bringing a surge of cooler air from the north and snow showers..mainly over the northern side of the state. There will be considerable rain (snow) shadowing over the lowlands south of Seattle, but Puget Sound convergence snow and other snowbands will be found over the northern half of western WA. Seattle should be prepared and SDOT should be particularly staged north of the ship canal. Wherever the convergence zone band sets up could get several inches.

Then there is a break early Monday, but then a warm front will approach during the afternoon. The cool air will hold in a while, particularly over NW WA, and there will be some initial snow--perhaps several inches in some locations---before it all turns to rain on Tuesday. Warmer air will move in on Tuesday and life will be back to normal. LOTS of snow in the mountains and eastern Washington on Tuesday.

This is a very difficult forecast with the snow hardly being uniform over the region. There is uncertainty...but the above is my best shot. We are not talking about a major snowstorm!

PS: I will be giving a public lecture--"The Secrets of Snow"--at Third Place Books in Lake Forest Park on December 17th at 7 PM, followed by a book signing. In this talk I will describe the unusual circumstances that have to come together for us to get a big snowstorm, details of convergence zone snows, the Fraser River Gap flow, arctic fronts, and more. My favorite topic.

Thursday, December 10, 2009

Another really cold day, although it warmed up a bit this afternoon. The air aloft was warmed significantly--by roughly 10F over the last 24 h, and surface stations are about 2-5F warmer than yesterday at the same time.

While bicycling into work this morning (it was 18F when I left my home!), I was warmed by the sight of steam fog over Lake Washington. It was surreal...sort of like the steam and fog coming out of some large witches brew. Devin Ellis sent me a picture snapped on his phone-as shown above. Steam fog occurs when cold air passes over much warmer water. The air temperature was around 20F and the water temperature according to the King County buoy was around 48F. You see steam fog during our primo cold air outbreaks...particularly early in the season when the water is fairly warm.

OK, but steam fog is not what you really want to know about...its the potential for snow. My friends in the National Weather Service have a "chance of snow" in the forecast for the entire weekend and on Monday. Can't argue with that...but lets try to be more specific. The computer models are not in agreement on Sunday and Monday, leaving us with some uncertainty.

There are basically two shots at snow: Sunday and late Monday. On Sunday, our first chance comes as a short wave disturbance aloft moves southward and crosses the region (graphic). The current forecast driven by the GFS model is not favorable for a general snowstorm..the disturbance is a little too far east and the amount of precipitation is light (check my book section on the optimal snow set up). The other NWS model (NAM) has more forcing over us. Considering the normally superior GFS-WRF run (WRF is a high resolution local model run at the UW), there would be only some scattered snow showers around here, with heaviest lowland snow perhaps in a Puget Sound convergence zone north of Seattle (graphic).But we get a second chance at the white stuff! On Monday a warm front will approach, with lots of precipitation (graphic, green and yellow are warmer air). Cold air will be in place--particularly over the northern portion of the state and it could start as snow...and perhaps last as snow for several hours (graphic).Eventually (on Tuesday) the atmosphere here will warm and the cold and snow will be gone..but before that we have two shots at it. I wish I could tie this up neatly for you...but I can't. Clearly, a better chance up in NW Washington. Mountains will surely get lots of snow, as should eastern WA.

And did I mention the potential heavy rain and a pineapple express on Tuesday? I better not talk about this right now...enough to think about....

PS: I will be giving a public lecture--"The Secrets of Snow"--at Third Place Books in Lake Forest Park on December 17th at 7 PM, followed by a book signing.

Wednesday, December 9, 2009

I get the feeling a lot of you want a big snowstorm. I think the Mayor and the Seattle DOT also want it, if only to prove they can get it right this time. (By the way, I have been really impressed with the proactive treatment by SDOT using brine solution on steep roadways---they are clearly trying--and it does help).

Is it possible we will see snow? Yes. Is a major snowstorm in the lowlands probable? Not at this time. Is there a lot of uncertainty? Yes. Will we get warmer by mid-week? Probably yes. Will there be lots of snow in the mountain and eastern WA? Almost certainly yes. Will plumbers make a lot of money when the temperatures warm up and frozen pipes start leaking. A certainty.

Another cold night in store. And another sunny day tomorrow (Thursday).Friday will be slightly warmer with some increasing high clouds.

Sunday a weak disturbance will move through and we will get some light snow in the mountains and some light snow showers scattered around the lowlands. The only real lowland accumulation could be in a Puget Sound convergence zone north of Seattle and south or over Everett...but that is not certain. See 24h snowfall ending 4 AM Monday below.

Sunday will be generally dry and a bit warmer.

The fun is late Monday/Tuesday. An approaching warm front will bring precipitation into our area...but it probably will warm things up enough to start most of the lowlands as rain--but some locations may see some snowflakes before it turns over. (graphic for 4 AM Tuesday below--green and yellow are warmer air)But if the system came in a little more to our south (as this morning's runs), it could draw in cold air and the event could start as snow. Finally, it all turns into warm rain.

The models have really been all over the place, so my confidence in the Monday/Tuesday situation is not great...this is my best shot at it. Above is the 24-h snowfall ending 4PM on Tuesday...lots of snow over the mts. and eastern WA. Not much over the lowlands...sorry.

A lot of you are wondering about snow. I have been wondering too. The problem is that the models are not consistent for this weekend and early next week. This morning our local model forced by the GFS..the NWS's best large scale forecast model, indicated a major snowstorm late Monday. But I don't trust any of it at this point and you shouldn't either. Thursday and Friday until dinnertime looks dry for western Washington...and cold. You can bank on that.

Will look at the new runs tonight and make a stab at a forecast. In any case, when you have the cold in place, things happen.

Tuesday, December 8, 2009

Tonight may end up the coldest night of the entire winter for many. Cold air has settled over the region and differences in pressure have decreased (see graphic of pressures over the region), resulting in weakening winds. Winds help to stir up the low-level atmosphere...mixing up warmer air from above the surface to the ground.

Why is the air warmer above the surface on these clear nights? Because the earth can effectively emit infrared radiation to space (better than the air) and thus the surface cools down faster. Thus, on clear, nearly calm nights we can develop inversions in which the temperature WARMS with height.

You can see the inversion forming tonight in the figure below, which shows conditions above North Seattle.Inversions act as stable layers or lids that keep the air from mixing and allows pollutant levels to rise. And this build up of pollutants increases further on cold nights when people run their heating units more and especially when they burn wood in their fireplaces and stoves. Burning wood injects a huge array of particles and toxic substances into the air. I know. A fire can be nice on a cold night and the odor even a bit attractive...but this is really bad stuff. Full of particles that interfere with lung function and chemicals that cause cancer.

As a result of the developing inversion and increasing woodburning, air quality is declining fairly rapidly in many locations. Take a look at the graphics for reporting stations in Everett, Lake Forest Park, and Bremerton. Air has either attained unhealthy status or will soon be there (see graphics).

The Puget Sound Clean Air Agency has placed a stage 2 burn ban out for Snohomish County. During such burn bans

No burning is allowed in any fireplace, pellet stove or wood stove (certified or not), unless it is your only adequate source of heat.

You can use natural gas or propane fireplaces.

No visible smoke is allowed from any solid fuel burning device at any time.

For more info on local air quality check their web site: http://www.pscleanair.org/ I think you can expect them to extend this band to other locations.

There have been a number of studies, some done at the UW, showing how bad wood smoke can be for vulnerable individuals (like those with asthma, breathing problems, or heart conditions). The smoke tends to settle in low spots...like hollows and valleys. The valley of Lake Forest Park is infamous for poor air. I live at the bottom of a hill and when people uphill from me use fireplaces..and particularly when they use wet scrap wood...the smoke becomes palpable in my home and very unpleasant. One time it even set off my fire alarms. I asked them to stop and they did.

But it is good to know that if you have some problem uphill neighbors sending smoke your way you can call the clean air agency and they will talk to those in the problem household. And if there is visible smoke they have the power to levy fines.

Monday, December 7, 2009

It was quite cold this morning, with temperatures dropping to the low 20s and even teens in some western Washington locations. You don't want to know how cold it is in eastern Washington! Tonight will be even colder.

Several people have asked...why was there little or no frost this morning, even though we had the coolest temps of the year so far? The answer: low humidity.

Our dew points have been very, very low. (Remember what dew point is? The temperature to which you have to cool the air down to get saturation. Below 32F we really should call it "frost point" but we never do). The dewpoints this morning were in the single digits and even below 0F for most of the region. So you would have to cool the air down that low to get frost...and we didn't. So the temperature remained well above the dewpoint and we didn't see any frost or fog. Here are the current observations....same story tonight...LOW dewpoints

That is good thing. We had lots of frost on Saturday morning and slippery roads and accidents were everywhere. I almost spun out myself. One woman was killed. Never forget, roadway icing is the number one weather killer in our area. More than floods, more than windstorms. I put a whole section on this in my book for a reason. I have also created a web page just on this topic (sponsored by Washington DOT):http://www.atmos.washington.edu/~cliff/Roadway3.html

Most of the time such accidents can be avoided by driving slower. And make sure you have decent tires and get Vehicle Stability Control on your new or used car if you can afford it. Remember: the road temps on clear nights can be colder by 2-5F than what you see on your car thermometer, the official weather reports (which are for locations about 6 feet above the surface), and certainly the often inaccurate bank thermometer. And bridges ice up soon because they don't get the heat conducted from the soil.

Air quality is still quite good, but it may decline in time. A good place to check on it is the web site of the Puget Sound Clean Air Agency (http://www.pscleanair.org/)

Finally, some of your have noted that PROBCAST is going 7F for Seattle tomorrow. Probcast is wrong, trust me. And I know why...we are using an early version of our current computer models to drive it and it is not dealing with this cold period correctly. As soon as I can secure funding for new computers I will upgrade the whole system--so don't trust the low temperatures. Probcast is an experimental system.

Finally, what about snow? Well, to get snow in our area you need cold and wet and it is very hard to get both together. Well, we have cold now...all we need is wet. The big snow threats are moving into and out of cold periods. We got in without much, but what about the exit period? Thursday could have some scattered snow showers, but the real threat is over the weekend as we transition to a warmer, wetter regime...more on that tomorrow.